module.exports = function base64_decode(encodedData) {

  var decodeUTF8string = function (str) {
    return decodeURIComponent(str.split('').map(function (c) {
      return '%' + ('00' + c.charCodeAt(0).toString(16)).slice(-2);
    }).join(''));
  };

  if (typeof window !== 'undefined') {
    if (typeof window.atob !== 'undefined') {
      return decodeUTF8string(window.atob(encodedData));
    }
  } else {
    return new Buffer(encodedData, 'base64').toString('utf-8');
  }

  var b64 = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=';
  var o1;
  var o2;
  var o3;
  var h1;
  var h2;
  var h3;
  var h4;
  var bits;
  var i = 0;
  var ac = 0;
  var dec = '';
  var tmpArr = [];

  if (!encodedData) {
    return encodedData;
  }

  encodedData += '';

  do {
    // unpack four hexets into three octets using index points in b64
    h1 = b64.indexOf(encodedData.charAt(i++));
    h2 = b64.indexOf(encodedData.charAt(i++));
    h3 = b64.indexOf(encodedData.charAt(i++));
    h4 = b64.indexOf(encodedData.charAt(i++));

    bits = h1 << 18 | h2 << 12 | h3 << 6 | h4;

    o1 = bits >> 16 & 0xff;
    o2 = bits >> 8 & 0xff;
    o3 = bits & 0xff;

    if (h3 === 64) {
      tmpArr[ac++] = String.fromCharCode(o1);
    } else if (h4 === 64) {
      tmpArr[ac++] = String.fromCharCode(o1, o2);
    } else {
      tmpArr[ac++] = String.fromCharCode(o1, o2, o3);
    }
  } while (i < encodedData.length);

  dec = tmpArr.join('');

  return decodeUTF8string(dec.replace(/\0+$/, ''));
}

